Open-water net pen aquaculture for species including salmon, sea bass, and sea bream presents specific welfare challenges related to sea conditions, parasite pressure, and escape risks.
Net pen welfare is shaped by the interaction between fish biology and the marine environment. In well-sited pens with good current flow, fish can maintain normal swimming behaviour and water quality is relatively good. In poorly sited or overcrowded pens, waste accumulation beneath cages degrades water quality and increases disease pressure. Storm events cause net damage risking escapes and can drive fish against net walls causing injury. Parasite management in open systems is challenging because wild fish in the area act as natural reservoirs. Site selection, stocking density management, and integrated parasite control are the primary welfare levers in net pen systems.